import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
import java.nio.charset.StandardCharsets;

public class UdpEchoServer {
    private DatagramSocket socket=null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    //通过start 启动服务器的核心流程
    public void start() throws IOException {
        System.out.println("服务器启动!");
        while(true){
            //通过死循环不停的处理客户端的请求

            //1.读取客户端的请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            //上述收到的数据,是二进制byte[]的形式体现的,后续代码如果要进行打印之类的操作 需要将其转成字符串
            //构造string字符串            获取字节报的数据,从数组的0位置开始构造string,长度为字节报的长度
            String request = new String(requestPacket.getData(),0, requestPacket.getLength());

            //2.根据请求计算响应,由于此处是回显服务器,响应就是请求
            String response = process(request);

            //3.把响应写回到客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),response.getBytes().length
            ,requestPacket.getSocketAddress());//UDP是无连接的,所以要手动将客户端的请求的IP和端口号取出并包装到responsePacket里
            socket.send(responsePacket);

            //4.打印日志
            System.out.printf("[%s:%d] req=%s ,resp=%s\n",requestPacket.getAddress(),requestPacket.getPort()
            ,request,response);//获取IP地址和端口号,请求和响应
        }
    }

    private String process(String request){
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server =new UdpEchoServer(9090);
        server.start();
    }
}
